Installation for FrugalWare
+ added missing link in index.rst
* some gramatic and spelling fixes

Thx jamtur :)
* s/docker/Docker/
Fix typo in working with volumes doc page
add a simple note to suggest to the user to use RUN curl/wget/tool if the URL they need is behind auth
Merge pull request #3380 from SvenDowideit/add-no-auth-note

add a simple note to suggest to the user to use RUN curl/wget/tool if the URL they need is behind auth
Merge pull request #3312 from DeX77/master

 Installation for FrugalWare
Merge pull request #3371 from Grunny/volumes-typo-fix

Fix typo in working with volumes doc page