Update installation_usage_summary.md

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Merge pull request #80 from Neymello/patch-1

Update installation_usage_summary.md
Changed page table operations to use ERT. Everything works
fine after the modification. A few cases not tested yet. Also, need to
get rid of some warnings (unused functions).
Merge branch 'master' of https://github.com/gparmer/Composite
Merge branch 'ppos' of https://github.com/gparmer/Composite

Conflicts:
	src/kernel/include/pgtbl.h
Fixed a bug in pgtbl_intern_prune. Tested and worked.
Fixed pgtbl_mapping_mod, which is used to update flags of an existing
mapping.

Now _all_ functions in pgtbl.h have been tested. We don't rely on
Linux pgtbl functions any more!
Merge pull request #82 from interwq/master

Page table manipulation functions update